This application is a continuation-in-part of application Ser. No. 895,280, filed Aug. 11, 1986, now abandoned.
The present invention relates to a method of and apparatus for applying adhesive onto webs of sheet material so that the webs may be adhered together, and in particular to such a method and apparatus in which the amount and location of adhesive applied onto flutes of single facers is very accurately controlled.
Prior machines for applying adhesive onto the flutes of a plurality of single facers of corrugated cardboard media, so that the single facers may be adhered in overlying relationship and to a facing to form a sheet of cardboard, use applicator rolls for applying adhesive onto the flutes, and one or more belts at a combiner bring the single facers into overlying and adhering relationship and pull the single facers across the applicator rolls and through the machine. The combiner belts are supported on and moved by drums, and the applicator rolls are normally driven by means of a direct drive between one of the drums and the rolls. Usually, one drum carries a sprocket connected by a chain to an input sprocket to a distributor, and sprockets carried by individual applicator rolls are connected by chains to an output sprocket from the distributor. Rotation of the combiner drum therefore rotates the applicator rolls, and the arrangement is such that a predetermined fixed mechanical relationship exists between the speeds of rotation of the applicator rolls and that of the drum.
A disadvantage of prior adhesive applying machines is that the ratio between the speed of rotation of the combiner drum and the speeds of rotation of the applicator rolls cannot readily be changed. Because of the direct drive between the drum and rolls via chains and sprockets, to change the ratio of the speeds requires the tedious procedure of changing the distributor input sprocket. However, changing the distributor input sprocket only serves to change the ratio of the speed between the drum and each roll by the same amount. It does not change the ratio of the speeds between the drum and individual ones of the rolls by selected amounts, since that may be accomplished only by also changing the sprockets on the rolls, and as applicator roll sprockets cannot readily be replaced, prior practice does not contemplate that they be changed. Instead, once selected the applicator roll sprockets are normally not changed except as may be required for replacement due to wear, and they usually are selected so that irrespective of the speed of rotation of the combiner drum, all of the applicator roll peripheries move at the same speed, so changing the distributor input sprocket only serves to uniformly change the speed of each applicator roll periphery.
The rationale behind rotating the applicator rolls by a direct drive between the rolls and a combiner belt drum is to obtain a direct correlation between the peripheral speeds of the rolls and the speed of travel of the single facers as they are pulled across the rolls. The single facers are pulled across the roll peripheries by the combiner belts, which ride on and are moved by the combiner drum, so it is assumed that, ideally, a known and direct relationship exists between the speed of travel of the single facers and the speed of rotation of the drum and, therefore, between the speed of the single facers and the speeds of the roll peripheries. However, the assumption ignores, and the technique cannot account for, slippage that occurs in practice between the belts on the drum and the single facers on the belts. Usually, the distributor input sprocket is selected to obtain a predetermined relationship between single facer and applicator roll peripheral speeds, such that the roll peripheries move slightly slower than the single facers to obtain a wiping action across the flutes, but because of slippage the relationship is impossible to maintain.
Because of the inability with prior machines to accurately control the speeds of the applicator roll peripheries with respect to the speed of travel of single facers moved across the peripheries, and to independently and accurately control the single facer/roll periphery speed relationship for each applicator roll to compensate for variations in flute configurations and consistencies, according to conventional practice an excess of adhesive is applied onto the flutes to ensure proper adhesion of the single facers one to the other despite misplacement of adhesive on the flutes as a result of variations in the speed relationship. This is accomplished by using applicator rolls that have either smooth or cellular peripheral surfaces, and by using a metering roll to doctor adhesive picked up by the applicator rolls in a manner to leave a film of adhesive of selected thickness on the peripheries for transfer to the single facer flutes. However, water comprises a substantial portion of the adhesive, and in addition to wasting adhesive, a consequence of transferring excess adhesive to the flutes is that the flutes are excessively moistened. The adhesive must be dried in the combiner to adhere the single facers together, so the more moisture that is applied onto the flutes, the greater the heat energy requirements to set the adhesive. More importantly, excessively moistening the flutes results in warping of the resulting cardboard material and "ribbing" on its outer facing or surface, which often makes it very difficult if not impossible to apply high quality printing or graphics onto the surface.